Well drilling and production

ABSTRACT

A method for drilling a well and for producing a well through a permafrost zone by maintaining at least a part of the well bore in the permafrost zone at a temperature of from about 14* to about 35* F.

United States Patent Luther E. Bartlett Dallas, Tex.

Nov. 13, 1969 Nov. 9, 1971 Atlantic Rlchfleld Company New York, N.Y.

inventor Appl. No. Filed Patented Assignee WELL DRILLING AND PRODUCTION 17 Claims, No Drawlngs U.S. Cl. 175/ 17, 175/72, l66/D1G. 1 Int. Cl. EZlb 7/00, E21b 21/04 Field 01 Search l66/D1G. 1;

[56] References Cited UNITED STATES PATENTS 2,193,219 3/1940 Bowie et a1. 175/17 2,621,022 12/1952 Bardill 175/17 3,179,528 4/1965 Holmgren 106/90 Primary Examiner-James A. Leppink Attorneys-Blucher S. Tharp and Roderick W. MacDonald ABSTRACT: A method for drilling a well and for producing a well through a permafrost zone by maintaining at least a part of the well bore in the permafrost zone at a temperature of from about 14 to about 35 F.

WELL DRILLING AND PRODUCTION BACKGROUND OF THE INVENTION Permafrost is defined as a permanently frozen layer at variable depths below the earth's surface in frigid regions. The permafrost layer is normally thought to be composed of frozen soil and rock and to also contain intervals of free iceand/or ice lenses. When the ice in the permafrost is melted, the soil and rocks are then freed to move and, in the case of awe bore drilled therethrough, tend to slough or otherwise cave into and fill the well bore. This sloughing phenomena therefore causes redrilling of substantial portions of the well bore and greatly extends the time and cost of drilling a well.

Heretofore it was thought that the problem of permafrost sloughing could be eliminated by artificially cooling the well bore to subzero temperatures. For example, it has been taught to precool well bores anywhere from -4' to -l C.

However, it was found that even with this excessive freezing approach the sloughing phenomena still occurred in many instances.

SUMMARY OF THE INVENTION It has now been discovered that permafrost contains some unfrozen water and that freezing of this water can cause sloughing of the permafrost soil and rock into the well bore in a manner similar to the sloughing caused by thawing the permafrost.

It has further been discovered that if at least a portion of the well bore in the permafrost zone is maintained substantially at a temperature from about 14 to about 35 F., sloughing of the pennafrost does not occur either from the thawing mechanism or the excessive freezing mechanism.

Accordingly, this invention relates to a method for drilling a well bore in the earth through a permafrost zone and a method for producing fluid from a well bore in the earth through a permafrost zone, both of which methods comprise in their improvement the maintenance of at least part of the well bore walls in the permafrost zone at a temperature from about 14 to about 35 F.

This invention is, therefore, useful in shortening both the time and cost for drilling a well in permafrost and in extending the producing life of a well drilled through a permafrost zone.

Accordingly, it is an object of this invention to provide a new and improved method for drilling a well bore through a permafrost zone subject to sloughing on thawing or excessive freezing. It is another object to provide a new and improved method for preventing permafrost sloughing while drilling a well bore through a permafrost zone. It is another object to provide a new and improved method for producing a well through a zone of permafrost subject to sloughing on thawing or excessive freezing. It is another object to provide a new and improved method of preventing pennafrost sloughing in a well bore that is producing through a permafrost zone.

Other aspects, objects, and advantages of this invention will be apparent to those skilled in the art from this disclosure and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION According to this invention there is provided a method for drilling a well bore through a permafrost zone. There is additionally provided a method for producing fluid such as oil or gas, particularly a warm fluid, i.e., one which is at a temperature of at least the melting point of water, from a well bore in the earth through a permafrost zone. Both of these methods, when practiced in accordance with this invention, prevent sloughing of the permafrost soil and rock into the well bore due to either thawing of the permafrost or excessive freezing of the permafrost and the consequent freezing of free water present in the permafrost. In both methods, sloughing is prevented and the borehole maintained intact by maintaining the well bore walls in at least part of the permafrost zone at a temperature of from about 14 to about 35 F., preferably from about l4 to about 32 F.

Although the entire well bore or at least the entire permafrost zone in the well bore can be maintained in the required temperature range, it is also within the scope of this invention to maintain only an effective sloughing preventive part of the permafrost zone in this temperature range. Thus, it is within the scope of this invention to maintain only a sufficient part of the permafrost well bore in this temperature range so long as sloughing is prevented and this part is considered to be an effective sloughing preventive part of the well bore in the permafrost zone. It should be emphasized, however, that besides applying only to a part of the well bore in the permafrost zone, this invention also applies to the complete length of well bore in the pennafrost zone as well as to the entire length of the well bore in the earth. Generally, at least a major portion of the well bore in the pennafrost zone will be maintained within the required temperature range.

The drilling method of this invention can be practiced in any manner which will maintain the required amount of well bore wall in the required temperature range. One particularly useful procedure for the drilling method is to take advantage of the drilling fluid added to the well bore at the surface of the earth to meet the normal requirements of the drilling operation. By this procedure the temperature of the drilling fluid added to the well bore is controlled so that the temperature of both the drilling fluid in the well bore and any other fluid which may intrude into the well bore from subsurface geological formations is in the required temperature range in at least an effective sloughing preventive part of the well bore in the permafrost zone. A particularly good approach with this procedure is to control the temperature of the drilling fluid added to the well bore so that the temperature of the added drilling fluid is a temperature within the required temperature range of from about 14 to about 35 F., preferably from about 14 to about 32 F when that drilling fluid is added to the well bore.

This invention is applicable to substantially any drilling fluid employed in the drilling operation and therefore applies to gaseous as well as liquid drilling fluids and particularly to water base liquid drilling fluids and hydrocarbon base liquid drilling fluids. The hydrocarbon base drilling fluid can be an oil base liquid containing at least one fluid loss control agent such as asbestos, asphalt, combinations thereof, and any other fluid loss control agent or agents known in the art. The drilling fluid can also be salt water having a freezing point of about 5 F. and containing at least one viscosity increasing agent such as clays, e.g. bentonite; gums, e.g., guar gum; asbestos; and the like. The salt water base can contain any number of inorganic salts such as sulfates, phosphates, halides, and carbonates of alkali metals and alkali earth metals, particularly sodium chloride and calcium chloride. A particularly good oil base drilling fluid is Diesel oil, particularly Arctic grade, in combination with fluid loss controlling amounts and/or viscosity increasing amounts of at least one ticularly air blown asphalt.

In the method of this invention which relates to producing fluid from a well bore, the required temperature over the necessary portion of the well bore in the permafrost zone can be achieved in any manner known in the art such as by installing a refrigeration means, with or without insulation, in the well bore.

A particularly useful procedure for this method is the introduction of a fluid, gas and/or liquid, into the well bore and the controlling of the temperature of the introduced fluid to maintain the required portion of the well bore in the required temperature range. Ifdesired, the fluid can be circulated into and out of the well bore in the same manner as drilling fluid during the drilling operation. In this approach, it is also useful to maintain the introduced fluid at a temperature within the required temperature range when the fluid is first introduced into the well bore. The introduced fluid can be any drilling fluid, particularly the drilling fluid as defined hereinabove with respect to the drilling operation. The fluids can be oil, water, refrigerant, and the like in liquid and/or gaseous form.

of asbestos and asphalt, par- A particularly useful fluid is Diesel oil, preferably Arctic grade, which has been precooled or otherwise temperature controlled to be within the required temperature range when first introduced into the well bore.

The fluids introduced into the well bore in accordance with this invention, be they drilling fluids or otherwise, can include other conventional additives such as surface active agents, scale inhibitors, corrosion inhibitors, dispersants, deflocculants, and the like.

EXAMPLE Three boreholes were drilled in a permafrost region using a borehole diameter of 12% inches and drilling to a borehole depth of 2,500 feet. Substantially all of the 2,500 feet of borehole depth was permafrost.

In the drilling of each borehole, a drilling fluid was employed at the rate of 600 gaL/min. The drilling fluid for each borehole was composed of a water base with sufficient sodium chloride added thereto to give a freeze point of 12 F. and with from 15 to 25 lbs./bb1. of sodium bentonite added thereto. The amount of sodium bentonite was varied to maintain the viscosity of the drilling fluid added to each borehole the same for each borehole.

During the drilling process for each borehole, after each additional increment of 30 feet of new borehole was drilled, the drill pipe was raised 30 feet from the bottom of the borehole to add an additional length of drill pipe. Also during the drilling of each borehole, the drilling pipe was completely removed from the borehole eight times to exchange drilling bits.

1n the first borehole the drilling fluid, when added to the borehole, was at temperatures varying from 38 to 46 F. The drilling fluid, when recovered from the borehole, was no more than 1 or 2 F. higher than its temperature when first added to the borehole. During the drilling of this first borehole, whenever the drill pipe was completely removed for the exchange of bits, the permafrost soil and rock sloughed into the borehole filling the hole to a height from 50 to 300 feet from the bottom of the hole as it existed when the drill pipe was first removed. Each time the drill pipe was raised 30 feet to add an additional section of drill pipe, this 30 feet was filled in with sloughing permafrost and in some cases the drill pipe was lifted even further by the upward push of additional permafrost sloughing into the well bore. Because of the sloughing problems encountered as described above, the first well bore took 25 days of drilling to reach the 2,500 foot depth.

In drilling the second well bore, the drilling fluid was precooled to l F. before being introduced into the well bore and was no more than 1 to 2 F. warmer when recovered from the borehole. The same sloughing problems were encountered as described hereinabove with respect to the first well bore when the drilling pipe was lifted 30 feet to make a new connection and when the drilling pipe was removed from the borehole to exchange bits. The drilling time required to reach a depth of 2,500 feet with the F. drilling fluid was also 25 days. Thus, it can be seen that no improvement in the sloughing problem was achieved with the l0 F. drilling fluid.

The third borehole was drilled with drilling fluid varying in temperature from about to 26 F. when first introduced into the borehole and which was no more than 1 or 2 F warmer when recovered from the borehole. ln drilling this well bore, no sloughing was encountered and the 2,500 ft. drilling depth was reached in 4 days.

it can be seen from the above data that excessive freezing of the well bore can create stresses in the well bore walls which cause sloughing problems similar to those encountered when the permafrost is thawed. Thus, uncontrolled cooling of the drilling fluid does not solve the sloughing problem. It can further be seen that controlled cooling of the drilling fluid in accordance with this invention decreased the required drilling time very substantially, i.e., from days to 4 days, and

thereby generated a correspondingly substantial savings in drilling costs.

Reasonable variations and modifications are possible within The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for one of drilling a well bore in the earth through a permafrost zone and for producing fluid from a well bore in the earth through a permafrost zone, the improvement comprising maintaining the well bore in at least part of said permafrost zone at a temperature of from about 20 to about 26 F.

2. In a method for drilling a well bore in the earth through a pennafrost zone subject to sloughing on thawing or excessive freezing, said drilling being conducted with the aid of a drilling fluid, the improvement comprising controlling the temperature of the added drilling fluid so that the temperature of both the drilling fluid and any other fluid in at least an effective sloughing preventive part of the well bore in the permafrost zone is at a temperature of from about 20 to about 26 F.

3. A method according to claim 2 wherein said added drilling fluid is temperature controlled to be at a temperature of from about 20 to about 26 F. when added to said well bore.

4. A method according to claim 2 wherein said added drilling fluid is temperature controlled to be at a temperature of from about 20 to about 26 F. when added to said well bore.

5. A method according to claim 2 wherein said drilling fluid is one of a water base liquid and a hydrocarbon base liquid.

6. A method according to claim 2 wherein said drilling fluid is an oil base liquid containing at least one fluid loss control agent.

7. A method according to claim 6 wherein said oil is Diesel oil and said fluid loss control agent is one of asbestos, asphalt, and combinations thereof.

8. A method according to claim 2 wherein said drilling fluid is salt water having a freezing point of about 5 F. and contains at least one viscosity increasing agent.

9. A method according to claim 8 wherein said salt water contains at least one of NaCl and CaCl,, and said viscosity increasing agent is bentonite.

10. In a method for producing warm fluid from a well bore through a permafrost zone subject to sloughing on thawing or excessive freezing, the improvement comprising introducing a fluid into said well bore, and controlling the temperature of said introduced fluid to maintain the well bore in at least an effective sloughing preventive part of said permafrost zone at a temperature of from about 20 to about 26 F.

11. A method according to claim 10 wherein said introduced fluid is a liquid that is circulated into and out of said well bore.

12. A method according to claim 10 wherein said introduced fluid is passed into said well bore at a temperature of from about 20 to about 26 F.

13. A method according to claim 10 wherein said introduced fluid is passed into said well bore when at a temperature of from about 20 to about 26 F.

14. A method according to claim 10 wherein said introduced fluid is a drilling fluid selected from the group of a water base liquid and a hydrocarbon base liquid.

15. A method according to claim 10 wherein said introduced fluid is a liquid or gas that contains substantially no additives.

16. A method according to claim 15 wherein said fluid is at least one of oil, water, and refrigerant.

17. A method according to claim 15 wherein said fluid is substantially precooled Diesel oil. 

2. In a method for drilling a well bore in the earth through a permafrost zone subject to sloughing on thawing or excessive freezing, said drilling being conducted with the aid of a drilling fluid, the improvement comprising controlling the temperature of the added drilling fluid so that the temperature of both the drilling fluid and any other fluid in at least an effective sloughing preventive part of the well bore in the permafrost zone is at a temperature of from about 20* to about 26* F.
 3. A method according to claim 2 wherein said added drilling fluid is temperature controlled to be at a temperature of from about 20* to about 26* F. when added to said well bore.
 4. A method according to claim 2 wherein said added drilling fluid is temperature controlled to be at a temperature of from about 20* to about 26* F. when added to said well bore.
 5. A method according to claim 2 wherein said drilling fluid is one of a water base liquid and a hydrocarbon base liquid.
 6. A method according to claim 2 wherein said drilling fluid is an oil base liquid containing at least one fluid loss control agent.
 7. A method according to claim 6 wherein said oil is Diesel oil and said fluid loss control agent is one of asbestos, asphalt, and combinations thereof.
 8. A method according to claim 2 wherein said drilling fluid is salt water having a freezing point of about 5* F. and contains at least one viscosity increasing ageNt.
 9. A method according to claim 8 wherein said salt water contains at least one of NaCl and CaCl2, and said viscosity increasing agent is bentonite.
 10. In a method for producing warm fluid from a well bore through a permafrost zone subject to sloughing on thawing or excessive freezing, the improvement comprising introducing a fluid into said well bore, and controlling the temperature of said introduced fluid to maintain the well bore in at least an effective sloughing preventive part of said permafrost zone at a temperature of from about 20* to about 26* F.
 11. A method according to claim 10 wherein said introduced fluid is a liquid that is circulated into and out of said well bore.
 12. A method according to claim 10 wherein said introduced fluid is passed into said well bore at a temperature of from about 20* to about 26* F.
 13. A method according to claim 10 wherein said introduced fluid is passed into said well bore when at a temperature of from about 20* to about 26* F.
 14. A method according to claim 10 wherein said introduced fluid is a drilling fluid selected from the group of a water base liquid and a hydrocarbon base liquid.
 15. A method according to claim 10 wherein said introduced fluid is a liquid or gas that contains substantially no additives.
 16. A method according to claim 15 wherein said fluid is at least one of oil, water, and refrigerant.
 17. A method according to claim 15 wherein said fluid is substantially precooled Diesel oil. 